1. Field of the Invention
The present invention relates to a magnetic recording medium, particularly a film type multi-layered magnetic recording medium which has an excellent recording or reproducing capability for high density magnetic recording such as digital recording, analogue recording or PCM (Pulse Code Modulation).
2. Description of the Prior Art
The ability of a magnetic recording medium is rated by the information storing capacity per unit area, that is, the recording density.
In order to increase the recording density, the prevailing opinion so far, both experimental and theoretical, has required a higher antimagnetic force (Hc) and thinner layer of the medium. This view has been based on the idea of utilizing the magnetic recording phenomenon by magnetizing the longitudinal component of the magnetic medium, that is by employing the horizontal magnetizing mode effectively.
Accordingly, the conventional coated magnetic recording media that were suited for analogue recording, for example, the medium produced by vertically arranging magnetic grains on a horizontally arranged magnetic grain layer on a substrate, or that suited for digital recording, for example the medium produced by arranging magnetic grains at random or horizontally. When these magnetic recording media are applied for high density recording, the residual magnetic poles are facing each other. This cause a state in which the magnetic poles strongly repel each other and the maximum value is around the center of the transfer of the demagnetizing field within the magnetic layer of the medium. Consequently, the distribution of magnetization is modified to that with a gradual gradient, and thus, in a high density magnetic recording where this transfer area is aligned with a slight shift, the amplitude, i.e. the magnetization rate, diminishes as the recording density is increased. Under these circumstances, to realize high density recording, an increase of the antimagnetic force of the medium or thinning of the film is applied to diminish the demagnetizing function.
However, thinning of the film causes problems such as the decrease of productivity, mechanical strength or the output power. Particularly in the case of a coated film, thinning the film to 0.8 micrometer or less lowers the mechanical strength. Furthermore, the increase of the antimagnetic force and thinning of the film creates problems in the relation of the magnetomotive force between the magnetic medium and the magnetic head at the time of write-in and read-out, SN ratio of the reproduced signal, AC or DC noise and the coarseness of the magnetic medium surface.
Moreover, such magnetic coating materials generally have the disadvantage that drying or hardening the coated film material after forming it coarsens the film surface. The cause thereof is thought to be that a solvent included in the coated film material serves to agitate the magnetic grains with whirling when the solvent evaporates. Accordingly, in the conventional method, after the above-stated process, the quality of the surface is improved by such methods as polishing or calendering, etc.
Whichever case, the conventional magnetic recording medium is characterized by the emphasis of either its horizontal or its vertical component, but it has never been attained the increase of the magnetic recording characteristic of both the horizontal and the vertical component, that is, the angular ratio (Br/Bs) of each. (Br denotes the magnetic flux density and Bs denotes the maximum magnetic flux density. The angular ratio: Br/Bs=1 is the ideal state.)